Fiberglass comes in many shapes and sizes and can be used for a variety of applications. A general discussion of fiberglass manufacturing and technology is contained in Fiberglass by J. Gilbert Mohr and William P. Rowe, Van Nostrand Reinhold Company, New York 1978, which is herein incorporated by reference. During the preparation of fiberglass, whether by a blown fiber or continuous filament manufacturing process, the resulting glass fibers may easily be degraded in their strength characteristics by the self-abrasive motion of one fiber passing over or interacting with another. As a result of this self-abrasion, surface defects are caused in the fiberglass filaments resulting in reductions in overall mechanical strength. Furthermore, fiberglass which is destined for use as building insulation and sound attenuation is often shipped in a compressed form to lower shipping costs. When the compressed bundles of fiberglass are utilized at the job site, it is imperative that the fiberglass product recover a substantial amount of its precompressed thickness. Otherwise, loss of insulation and sound attenuation properties may result.
Traditionally, fiberglass has been treated with phenol/formaldehyde resole binders to alleviate the previously-mentioned defects. See, e.g. Phenolic Resins, A. Knop, et al., Springer-Verlag New York, c. 1985, p. 214-219. The phenol/formaldehyde binders utilized in the past have been the highly alkaline resole type which have the combined advantages of inexpensive manufacture and water solubility. Typically, the binders are applied to the fiberglass from aqueous solution shortly after the fibers have been produced, and cured at elevated temperature in a curing oven. Under the curing conditions, any remaining aqueous solvent is evaporated, and the phenol/formaldehyde resole cures to a thermoset state. The fibers in the resulting fiberglass product are thus partially coated with a thin layer of thermoset resin, which tends to accumulate at the junctions where fibers cross each other. The resulting product therefore not only suffers from less self-abrasion, but also exhibits higher recovery than a fiberglass product not incorporating a binder.
The alkaline phenol/formaldehyde resoles contain a fairly large excess of formaldehyde from the manufacturing process. This excess of formaldehyde has been taken advantage of by adding urea to the phenol/formaldehyde resole, resulting in a urea-extended resole. Urea-extended phenol/formaldehyde binders are more cost-effective than the straight phenol/formaldehyde resins, but exhibit some loss in properties as the urea content increases. Thus, efforts have been made to incorporate other resins which can enhance the properties of the binder.
In addition to the use of urea to extend phenol/formaldehyde resins for use in fiberglass binders, other nitrogen containing substances, such as dicyandiamide and melamine, have been utilized as well. Urea, and to a certain extent other amino group containing extenders, serve the dual function of providing a lower cost resin as well as reducing emissions of formaldehyde. Urea, for example, is available at approximately 20% of the cost of the alkaline phenol/formaldehyde resoles commonly used in fiberglass binders. Thus, an extension of the binder with 30% percent urea provides a substantial cost savings.
Moreover, urea is well known as a scavenger for formaldehyde, and incorporation of urea into the resin mix and allowing it to react in, the product being called a "prereact", is known to lower formaldehyde emissions up to approximately the stoichiometry of the urea/formaldehyde reaction. Although additional urea might further lower formaldehyde emissions, at same time, ammonia emissions and "blue smoke" are dramatically increased as the amount of urea or other nitrogenous substances approach and exceed the formaldehyde stoichiometry. Although efforts in the industry to eliminate or substantially reduce formaldehyde are well known, less well known is the fact that ammonia emissions are also under extreme scrutiny, with several states having exceptionally stringent requirements in this regard. Thus, it is desirable to lower both the formaldehyde and ammonia emissions from fiberglass binder compositions.
Further attempts have been made to reduce formaldehyde and ammonia emissions in addition to use of nitrogenous formaldehyde scavengers. Many such attempts include replacing all or substantial portions of the phenol/formaldehyde resin with other resins which are not formaldehyde-based resins. Examples of such substitutions include U.S. Pat. No. 5,340,868 where the traditional phenol/formaldehyde binders are replaced in whole by a binder containing a polycarboxy polymer, a .beta.-hydroxyalkylamide, and a trifunctional monomeric carboxylic acid. In U.S. Pat. No. 5,318,990 is disclosed a similar composition further employing an alkaline metal salt of a phosphorous-containing organic acid. Resin systems such as the foregoing have not met with commercial success, predominately due to the increased cost of the resins. Epoxy resin-based binders have the same drawbacks in addition to which they are generally not dilutable with water (reducible), and thus must be applied as dispersions.
In U.S. Pat. No. 5,108,798, a binder is proposed which contains a .beta.-hydroxyurethane functional material and a polycarboxylic acid. The binder is suggested for use alone or as a partial replacement for phenol/formaldehyde resins. The binder cost is increased, however, and formaldehyde emissions are only reduced relative to the proportion of phenol/formaldehyde solids replaced. In U.S. application Ser. No. 08/489,903 is disclosed addition of a polycarboxylic acid, which itself is incapable of curing, to a phenol/formaldehyde based binder. The binder displayed synergistically reduced formaldehyde emissions, and ammonia emissions were also reduced. However, polyacrylic acid is still a relatively high cost product, and thus overall binder cost is increased as well. Moreover, the levels of emissions are still in need of improvement.
The reaction sequences leading to formation of binder compositions have also been investigated. For example, in U.S. Pat. No. 4,757,108, a urea-extended phenol/formaldehyde resin was prepared by first reacting urea into a phenol/formaldehyde resole under acidic conditions, followed by neutralization and further addition of urea under alkaline conditions. However, such manipulations of the basic resin formulation are not known to produce other than relatively minor improvements in emissions. Replacement of traditional ammonium sulfate cure catalysts with acidic aluminum sulfate catalysts to reduce formaldehyde and ammonia emissions is disclosed in U.S. application Ser. No. 08/490,034. However, further improvement is needed.
Unless methods may be found to sharply curtail both formaldehyde and ammonia emissions, continued commercial viability of phenol/formaldehyde based binders is questionable. Moreover, wholesale substitution of other resin systems has, thus far, proved to be too costly, or to produce a cured binder with inadequate properties. Unfortunately, the consumer may have to bear these higher costs and lower performance factors in order to reap the environmental benefits of reduced emissions, unless a method of reducing emissions of the commonly used and relatively inexpensive phenol/formaldehyde based binders can be found.
It would be desirable to provide phenol/formaldehyde fiberglass binder compositions which are economical, which can be utilized with existing equipment, which can provide acceptable physical properties in the binder-coated fiberglass product, and which especially can provide these advantageous properties while sharply reducing formaldehyde and/or ammonia emissions.